I think there's no concept of vacuum's temperature at least for classical physics. Because temperature measures the movement and/or oscillation of particles, so no particles mean no temperature. It is like you say of the speed of a car, but if there's no car, the speed of nothing is meaningless.
I am not sure if in modern physics when they say the vacuum is not nothing, but somethingl, the temperature concept can be applied.

Quantum mechanics predicts that the lowest energy state of a vibrator has finite energy - the zero point energy. So atoms are predicted to continue to vibrate about their equilibrium position even at 0k. This is separate from the electronic energy - the total interaction energy of the electrons and nuclei at a fixed equilibrium geometry.
-Jim

If heat means the movement for patricles, plase clarify how this movemnt subsides by loss of heat as radiation, how can IR radiation be responsible?

Heat is one kind of energy which is the kinetic energy of the particles. In this case, this kind of energy is converted to radiation, the IR which is also another kind of energy.
The energy from the sun to reach earth is transfered by this way as well.

Heat is one kind of energy which is the kinetic energy of the particles. In this case, this kind of energy is converted to radiation, the IR which is also another kind of energy.
The energy from the sun to reach earth is transfered by this way as well.

Slightly OT, but kinetic energy is actually part of the internal energy of the system. Heat is the energy transfer that goes into raising the temperature of the system.

Edit: Even that's wrong. Heat flow acts to change the internal energy of a body, which may or may not result in a temperature increase. However, heat flow can only take place between bodies of different temperatures.

Arent Infra-red eletromagnetic waves? If that is so, can over wavelngth em waves also be considered to carry heat energY?

Say what? What is "over wavelength"?

What we call "radiant heat" is defined as the IR spectrum. This is because this is the range of the em spectrum that many of our common molecules (such as water and our skin) can receive the energy efficiently and convert to what we call "heat".

ALL em waves carry energy, but not all of this energy are converted efficiently to what we normally call heat. UV spectrum can heat up ordinary glass because it absorbs that spectrum efficiently, yet visible light has no affect on it.

What we call "radiant heat" is defined as the IR spectrum. This is because this is the range of the em spectrum that many of our common molecules (such as water and our skin) can receive the energy efficiently and convert to what we call "heat".

ALL em waves carry energy, but not all of this energy are converted efficiently to what we normally call heat. UV spectrum can heat up ordinary glass because it absorbs that spectrum efficiently, yet visible light has no affect on it.

This thread has become rather confusing and unfocused.

Zz.

Sorry, I meant 'other' wavlenght, I apologise if it caused any misconfusion

How can you hypothesize that enrgy can be Absorbed

As Energy is indirectly proportional to Wavelngth, shorter wavelngth Electromagnetic waves SHOULD also be considered to cause Heat

By the way, Can you please clarify what you mean by Heat in the above context

Also, I thnik that heat has to be related to movement of molecules since tempertaure is responsible for the physical state of matter (gas, liquid, solid)

Sorry, I meant 'other' wavlenght, I apologise if it caused any misconfusion

How can you hypothesize that enrgy can be Absorbed

Because that is what happens when light "disappears" when it hits objects. Do you have an alternative explanation for the blackbody radiation?

As Energy is indirectly proportional to Wavelngth, shorter wavelngth Electromagnetic waves SHOULD also be considered to cause Heat

Not it doesn't. You are forgetting one half of this important equation - THE NATURE OF THE RECEIVER. You may want to read our FAQ on photon transmission through a solid, especially on the PHONON spectrum of a material. The TYPE of material can also dictate if em radiation of a certain wavelength can be absorbed. No material has an infinite bandwidth of absorption. Your skin is obviously transparent to x-ray, which has a higher energy than visible light which is absorbed by the skin and turned into heat. So just because something has a higher energy doesn't mean it can "cause heat". Besides, you are ignoring the possibility that a certain range of wavelength can cause other phenomena such as molecular energy transition, photoemission, etc... Here, the absorbed energy does not go into heat.

By the way, Can you please clarify what you mean by Heat in the above context

Atomic or molecular KE or lattice vibrations, the SAME way it is defined in thermodynamics!

Zero point motion is predicted to persist to 0K. This energy cannot be radiated or lost any other way because there are no lower vibrational states available. But, the remaining motion occurs on a scale that is relatively small with respect to atomic sizes. The time-averaged atomic position remains fixed. The Lewis and Randall definition of 0K is that the entropy also be 0 and the substance be in a pure, perfect, crystalline state. As you get close to 0K, unpaired electron spin or nuclear spin can complicate matters, because mixtures of spin states can be obtained in the absence of a perturbing applied field.
-Jim

If you say all the EM radiations carry energy. How can the energy 'dissapper'? Isnt that violation of Enery-Mass equivalence

Not it doesn't. You are forgetting one half of this important equation
- THE NATURE OF THE RECEIVER.

All matter is supposed to be made of same material. And What do you mean by 'nature' in atomic terms.

The TYPE of material can also dictate if em radiation of a certain wavelength can be absorbed. No material has an infinite bandwidth of absorption. Your skin is obviously transparent to x-ray, which has a higher energy than visible light which is absorbed by the skin and turned into heat.

Well, this is purely hypothetical. X-rays are not absorbed by skin neither by bones. I recently postulated the reason for reflection of light